This disclosure relates generally to methods and systems for radio frequency (“RF”) shielding of electronic devices. Electronic devices are considered ubiquitous in today's society. Electronic devices are found everywhere and are used by everyone. Many electronic devices emit RF and many times can receive unintentionally spurious RF transmissions. For example, a common experience is the interference created when using a microwave and a cordless phone at the same time. The RF emissions from the microwave may interfere with the operation of the cordless phone and render the cordless phone inoperable until the microwave is turned off. Another common experience is the interference created when using a microwave and a WiFi router at the same time. In this example, the RF emissions from the microwave may interfere with the operation of the WiFi router and render the WiFi inoperable until the microwave is turned off or the WiFi router is switched to a different frequency. These are common examples that demonstrate that microwave ovens have RF emissions that may interfere with other devices that rely on RF for communications. More information about RF emissions from various electronic devices can be found in, “Study of RF Emissions of Various Electronic Devices Used by the Public” by Letertre et al., which is hereby incorporated by reference.
When referring to RF emissions that interfere with other electronic devices, sometimes it is referred to as radio frequency interference (“RFI”) or electromagnetic interference (“EMI”). Some may describe the emission of RF from an electronic device such as a microwave as RF leakage. However, in the present invention, the reference to radio frequency (“RF”) will refer to any of RF, RFI, RF leakage, EMI, RF energy, and spurious RF transmissions.
Hackers and/or enemies-of-the-state (“Hackers”) can utilize RF emissions to hack into systems, attack systems, spy/monitor on systems, or disrupt systems. Hackers may target electronic devices such as computers, routers, appliances, mobile phones, cordless phones, switches, computer monitors, game consoles, DVD players, control electronics and other electronic devices that are likely to emit RF signals that could be detected by sensors located onboard an enemy platform including but not limited to ground-based, airborne and/or space-borne platforms. The RF emissions from such devices may comprise keyboard strokes, computer monitor images, drawings, private data, business data, financial data, political data, defense data, internet URLs, URL history, IP addresses, cookies, real time data, stored data, meta data, device usage data, electronic records, electronic files, video, audio, control signals, or any type of data, information or signal that an electronic device may contain or emit.
A sophisticated enemy may use a sensor to detect RF emissions to insert an external RF hacking signal that may be comprised of one or more of viruses, noise, or other enemy directed RF signals. In other situations a sophisticated enemy may use the detected RF emission locations to direct a high energy laser (“HEL”) or an IREB (Intense Relativistic Electron Beam) system at those locations to physically destroy the electronic device. In other situations a sophisticated enemy may use a sensor to detect and monitor the RF emissions from certain electronic devices for intelligence purposes. Examples of where an enemy or hacker may be interested in RF emissions might be at a utility plant (i.e. electric, gas, water, solar, oil etc. . . . ) or at a corporate competitor. Hackers may detect RF emissions and use techniques mentioned above to disrupt or destroy elements of the utility plant.
In order to control RF/EMI, an industry has developed around shielding materials. Shields are measured by its “shielding effectiveness” (SE). An electro-magnetic (EM) shield is essentially any barrier placed between an EM emitter and a receptor, and it is designed to reduce the field strength of the emitter. The losses in EM emitter field strength are a function of the barrier's electrical and physical characteristics, such as its permeability, conductivity, and thickness; the frequency of the EMI; and the distance from the EMI source to the barrier/shield. The total SE of the shield is the sum of the reflection, absorption, and re-reflection losses. For more information see “Eyeing EMI/EMC In RF Designs,” by Jack Browne, Microwaves & RF (www.mwrf.com), June 2011, which is hereby incorporated by reference.
One method of shielding electronic devices comprises placing the electronic device in a box made of metal such as aluminum, steel or copper. In this method the electronic device continues to emit RF, however most of the RF emission is contained inside the box and not allowed to escape the box. Other methods include placing the electronic device in an enclosure made of metal screen such as a Faraday cage. Other methods include shielding entire rooms with metal and placing several electronic devices in such rooms. Shielding material may be made of metal, metal screen, woven-in metallic fabric, foam, or can be a metalized paint. In a building, windows can have special metallic louvers or embedded metal screens to minimize RF leakage. All of these methods are referred to as passive shielding solutions. The problem with passive shielding solutions is that RF still leaks. In other words, the RF signals still escape from the enclosure. Generally these passive shielding solutions dampen but do not eliminate RF emissions.
Shielding has also been used on individual components of a circuit board. Again this approach is considered passive shielding. Even encasing a component in metal does not eliminate the RF emission completely.